The scratch resistance of polymers has been the subject of numerous studies that have led to the characterization of plastic and fracture phenomena during scratching. Viscoelastic and viscoplastic behavior during scratching have been related to dynamic mechanical properties that can be measured via dynamic nano-indentation testing. Yet, an understanding of the origin of the fracture phenomena in a polymer, such as poly-methylmethacrylate(PMMA), during scratching remains approximate. Parameters like tip geometry and size, scratch velocity and loading rate, and applied strain and strain rates, have been considered critical parameters for the fracture process, but no correlation has been clearly established.
Perhaps the oldest way for measuring the hardness of a material is based on a scratch test. Mineralogists first developed this kind of testing to evaluate the hardness of stones. The hardness scale that resulted from this work was based on the ability of one material to scratch or to be scratched by another. The scratch test has also been found to have applications in understanding the fundamental mechanisms of wear adhesion. Scratching, abrasion, and wear are all factors that diminish the properties of a surface.
In recent years the mechanical properties of polymers have been studied. Polymer materials are useful as surface coatings due to low cost and because they can be formed or molded easily. Nevertheless, their useful life is often limited by poor mechanical properties. For example, automotive paints are subject to numerous forms of degradation. In particular, scratching and abrasion cause degradation of appearance and loss of optical performance of these materials.
In view of the foregoing, any improvements in scratch testing would be beneficial.